Subject: SOHO/LASCO HALO CME 110417 BACKSIDED

UCMEO 93001 10418 1730/
10417 61600 80142 3362/ 335// 113// 30467
10417 61505 81535 ///// 11185 1212/
99999

PLAIN

SOHO/LASCO observed a HALO CME on April 17, 2011.  Event is first seen in
C2 at 16:00 UT as a slow propagating loop emerging over the east and the south.
The event expands to a full HALO CME by 17:00 UT in the C2 field.
The event continues into the C3 field beginning 16:54 UT to 01:42 UT out to 22.9 Rsun.

Time/height measurements were marked to 5 points in C2 with speeds of 603.1 Km/sec
at position angle 179 degrees. The event is marked to 20 points in C3 where it
decelerates.  Speeds average through both fields to 467.0 Km/sec at PA 184 degrees.
Acceleration -9.16 m/sec^2.

STEREO COR2 B shows a large burst beginning 15:05 UT in the ENE field.  COR2 A sees this
CME at 15:54 UT in the West.  The 16:54 UT frame shows clear 'smoke ring' characteristics.
EUVI 195 B 15:05 UT shows a dimming and flare of AR11185 (?) in the NE quadrant near the limb.
SDO/AIA 193 shows a filament eruption at 14:42 UT near the west limb a South 32 degrees.
Material from this eruption may be associated with the HALO. 

These events are most probably the cause of the HALO event seen in LASCO.

The observation of this event is considered 'FAIR'. This CME is determined a BACKSIDED event.

Images and movies and time/height information for this event is available on the web at:

http://umbra.nascom.nasa.gov/lasco/observations/halo/2011/110417/


Best regards,

Kevin Schenk
Solar Heliospheric Observatory
EIT and LASCO Operations
NASA-Goddard Space Flight Center, USA

BT